Parkinson's disease is a progressive neurodegenerative disease, and is characterized by loss of nigrostriatal dopaminergic nerves (dopaminergic neurons). It has been confirmed through clinical studies made until now that a motor symptom of a Parkinson's disease patient is improved by transplantation of fetal midbrain cells. Based on this fact, cell replacement therapy is presumed to be employed as a treatment method for Parkinson's disease.